Arylaldehydes-pentafluorophenyl hydrazones as second-order nonlinear optical chromophores: A novel approach for remarkably defeating the nonlinearity-transparency trade-off

Article abstract of DOI:10.1246/cl.2002.232

A series of new arylhydrazone chromophores containing pentafluorophenyl as electronic acceptor are synthesized and found to exhibit significantly blue-shifted absorption in comparison with the corresponding 4-nitrophenyl analogues while keeping β value in

Full text of DOI:10.1246/cl.2002.232

232
Chemistry Letters 2002
Arylaldehydes-pentafluorophenyl Hydrazones as Second-order Nonlinear Optical Chromophores:
A Novel Approach for Remarkably Defeating the Nonlinearity-transparency Trade-off
Jianli Hua, Wei Zhang, Zhen Li, Jingui Qin,ꢀ Yaochun Shen, Yu Zhang,y and Zuhong Luy
y
Department of Chemistry, Wuhan University, Wuhan 430072, P. R. China
yNational Laboratory of Molecular and Biomolecular Electronics, Southeast University, Nanjing 210096, P. R. China
(Received September 10, 2001;CL-010885)
A series of new arylhydrazone chromophores containing
pentafluorophenyl as electronic acceptor are synthesized and
found to exhibit significantly blue-shifted absorption in compar-
ison with the corresponding 4-nitrophenyl analogues while
keeping ꢀ value in the same order, and this may provide a new
opportunity for defeating nonlinearity-transparency trade-off in
designing second-order nonlinear optical chromophores.
Organic second-order nonlinear optical (NLO) materials
have been the subject of intense investigations owing to their
exceptionally large nonlinearity and ultrafast response times.1
These materials have potential applications in areas such as
telecommunications, optical information processing and data
storage.2 One of the major challenges in this research is to design
and synthesize second-order NLO chromophores possessing
simultaneously large first-order molecular hyperpolarizability
(ꢀ), high thermal stability and good transparency.3 To date, most
highly nonlinear optical second-order chromophores have been
Scheme 1.
constructed by following the ‘‘ꢁ-donor linked to ꢁ-acceptor
through a ꢁ-backone’’ prescription. An intriguing question,
however, centers around the possibility of using modification in
the ‘‘NLO-inactive’’ ꢂ-framework to indirectly affect the ‘‘NLO-
active’’ ꢁ-system. Electronegative fluorine substituted systems,
that are weak ꢁ-donors and strong ꢂ-acceptors, could serve as
such prototypical moieties. ZINDO-SOS theoretical calculation
results strongly suggest that so-called inductive acceptors can be
used to produce highly efficient chromophores and the ꢀvalues of
the chromophores containing pentafluorophenyl acceptor are
approximately half as potent as those with a 4-nitrophenyl
acceptor.4
Recently, Alain reported that push-pull diphenylpolyenes
with a trifluoromethyl acceptor moiety can offer promising
opportunities in terms of transparency-efficiency trade-off and
have a particular interest for applications based upon cascading
processes.5 Jen also reported that the incorporation of this type of
chromophores based on the ꢃ-perfluoroaryldicyanovinyl electron
acceptors into polyquinoline led to both high electro-optical
property and low optical loss.6 On the other hand, Zyss et al. have
reported7 that 1,3-diphenylhydrazones, which exhibit similar
transparency and larger static first-order hyperpolarizability ꢀ0 as
compared to the corresponding diene derivatives, offer a slight
improvement of the nonlinearity-transparency trade-off. Here, we
report the first synthesis and their ꢀ values of a series of new
arylhydrazone chromophores (2a-2d in Scheme 1) with penta-
fluorophenyl as an electron acceptor.
ethanol. We also synthesized the corresponding 4-nitrophenyl-
hydrazone compounds (3a-3d in Scheme 1) for the purpose of
comparison. The spectral data and the results of elemental
analysis for all of the products were consistent with the expected
structures.8
The ꢀ values of the chromophores 2a-2d and 3a-3d were
measured by Hyper-Rayleigh Scattering (HRS) technique9 in
methanol using the fundamental excitation wavelength of
1064 nm. The known ꢀ value for p-nitroaniline (p-NA) in
methanol (34:5 Â 10À30 esu)10 was used as an external reference.
The measured hyperpolarizabilities ꢀ and the static ꢀ0 obtained
from the two-level modulation of these compounds as well as
their absorption maxima (ꢄmaxÞ are given in Table 1.
For a given donor and conjugated bridge, it has been found
that the ꢀ values of the arylhydrazones with pentafluorophenyl
acceptor are similar to those of the corresponding 4-nitrophenyl
analogues, and the results are in consistent with the prediction by
ZINDO-SOS theoretical calculation.4 However, it is very
interesting to note that 2a-2d show dramatically blue-shifted
absorption when compared with the corresponding 4-nitro-
phenyl analogues: 87 nm for 2a;92 nm for 2b;91 nm for 2c;
32 nm for 2d. UV-Vis absortion phenomena of 2a-2d highlight
the unusual structure and properties of pentafluorophenyl
acceptor and indicate that the pentafluorophenyl group as the
electron acceptor give rise to better transparency.
On the other hand, by comparison of 3a with 4-(N; N-
dimethylamino)-40-nitrostilbene (DANS) and 4-(N; N-dimethyl-
amino)-40-nitroazobenzene (DANAB), it can be seen that trans-
parency of 3a is similar to that of DANS but better than that of
DANAB, while their ꢀ0 values are comparable. The hydrazones
Four arylaldehydes-pentafluorophenyl hydrazones (2a-2d)
were prepared by the condensation reaction of the corresponding
arylaldehydes and pentafluorophenylhydrazine in anhydrous
Copyright Ó 2002 The Chemical Society of Japan

Chemistry Letters 2002
Table 1. Optical properties of 2a-2d and 3a-3d
233
(1994).
V. Alain, S. Redoglia, and M. B. Desce, Chem. Phys., 245, 51
(1999).
X. Wu, J. Wu, Y. Liu, and A. K.-Y. Jen, Chem. Commun.,
1999, 2391
max/nm ꢀa (10À30 esu)
5
6
7
8
ꢄ
c
Chromophores
ꢀ0 (10À30 esu)
in methanol at ꢄ ¼ 1064 nm
2a
3a
2b
3b
2c
3c
2d
344
431
331
423
319
410
439
471
474
438e
370
161
329
112
147
64
165
199
279
84
95
62
46
37
57
53
55
55d
42d
16
J. Zyss, ‘‘Molecular Nonlinear Optics,’’ Academic Press,
New York (1994), pp 149–150.
The yield, melting point, IR (KBr, cmÀ1Þ, NMR (300 MHz),
MS, and elemental analysis data for these compounds are as
follows: 2a: yield 86%;mp 171–172 ꢁC ;IR 1666 (-C ¼N),
3352 (N-H); 1H-NMR (CDCl3) ꢅ2.99(s, 6H), 6.69(d, J ¼ 9:0,
2H), 7.03(s, 1H), 7.51(d, J ¼ 9:0, 2H), 7.74(s, 1H);
MS(FAB), m=z: 329, 100%. Anal. Calcd for C15H12N3F5:
C, 54.71;H, 3.64;N, 12.76%. Found: C, 55.02;H, 4.15;N,
12.85%. 2b: yield 89%;mp135–136 ꢁC;IR 1662(C ¼N),
3317(N-H); 1H-NMR (CDCl3Þ ꢅ 0.84(t, 3H), 1.32(m, 6H),
1.86(m, 2H), 4.24(t, 2H), 7.28–7.36(m, 4H), 7.72–7.84(m,
2H), 7.88(s, 1H), 8.08(s, 1H), 8.24(s, 1H);MS(FAB), m=z:
459, 100%. Anal. Calcd for C25H22N3F5: C, 65.36;H, 4.79;N,
9.15%. Found: C, 65.15;H, 4.95;N, 8.75%. 2c: yield 73%;
mp 120–121 ꢁC;IR 1664(-C ¼N), 3358 (N-H); 1H-NMR
(CDCl3) ꢅ 3.84(t, 3H), 6.91(d, J ¼ 9:0, 2H), 7.15(s, 1H),
7.56(d, J ¼ 9:0, 2H), 7.78(s, 1H);MS(FAB), m=z: 316, 100%.
Anal. Calcd for C14H9F5N2O: C, 53.16;H, 2.84;N, 8.86%.
Found: C, 53.45;H, 3.15;N, 8.85%. 2d: yield 79%;mp 193–
194 ꢁC;IR 1664(-C ¼N), 3242(N-H); 1H-NMR(DMSO) ꢅ
1.12(t, 3H), 3.34(m, 6H), 6.76(d, 2H), 7.60–7.76(m, 6H),
8.10(s, 1H), 10.4(s,1H);MS(FAB), m=z: 477, 100%. Anal.
Calcd for C23H20F5N5O: C, 57.86;H, 4.19;N, 14.67%.
Found: C, 57.45;H, 4.55;N, 14.85%. 3b: yield 81%;mp 151–
152 ꢁC;IR 1359, 1540(-NO 2Þ, 3253(N-H); 1H-NMR (CDCl3)
ꢅ 0.85(t, 3H), 1.31(m, 6H), 1.88(m, 2H), 4.34(t, 2H), 6.99(d,
1H), 7.18–7.53(m, 4H), 7.92–8.03(m, 2H), 8.09–8.21(m, 4H),
8.62(s, 1H), 10.09(s, 1H);MS(FAB), m=z: 414, 100%. Anal.
Calcd for C25H26N4O2: C, 72.46;H, 6.28;N, 13.52%. Found:
3d
DANAB
DANS
p-NA
97b
73b
34
aꢀ values measured by HRS technique in methanol using the
fundamental excitation wavelength of 1064 nm. bꢀ measured
by EFISH in chloroform using the fundamental excitation
wavelength of 1300 nm.10 c,dDispersion-corrected ꢀ values
calculated by using an approximate two-level model (d see
Reference 10). eMeasured in chloroform.
seem then to offer interesting nonlinearity-transparency compro-
mise as compared to the corresponding stilbene and azobenzene
derivatives. In addition, 2a-2c exhibited also 26–51 nm blue-
shifted absorption in comparison with p-NA, and their ꢀ values
are 2–5 times higher than that of p-NA. All the above results
suggest that arylhydrazone chromophores with pentafluorophen-
yl moieties exhibit better optimization of the nonlinearity-
transparency trade-off.
In summary, we have synthesized a series of new
arylhydrazone chromophores containing pentafluorophenyl as
electron acceptor. They all show remarkablely blue-shifted
absorption in comparison with the corresponding 4-nitrophenyl
analogues and provide a new approach for turning the
nonlinearity-transparency trade-off.
ꢁ
C, 72.25;H, 6.31;N, 13.35%. 3d: yield 76%;mp 197–198 C;
IR 1340, 1522 (-NO2Þ, 3238 (N-H); 1H-NMR (DMSO) ꢅ
1.12(t, 3H), 3.12(m, 4H), 3.52(t, 2H), 6.76(d, J ¼ 10, 2H),
7.16(d, J ¼ 10, 2H), 7.68–7.76(m, 6H), 8.04–8.12(d, 2H),
8.16(s, 1H), 11.32(s, 1H);MS(FAB), m=z: 432, 100%. Anal.
Calcd for C23H24N6O3: C, 63.89;H, 5.56;N, 19.44%. Found:
C, 63.45;H, 5.75;N, 19.25%.
The work was supported by a grant from the National Key
Fundamental Research Program of China and by National
Science Foundation of China.
References and Notes
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2
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